The injection of CO₂ to displace CH₄ in coal seams is an effective method to exploit coalbed methane (CBM), for which the CO₂ injection temperature and pressure are important influential factors. We performed simulations, using COMSOL Multiphysics to determine the effect of CO₂ injection temperature and pressure on CO₂-enhanced coalbed methane (CO₂-ECBM) recovery, according to adsorption/desorption, seepage, and diffusion of binary gas (CO₂ and CH₄) in the coal seam, and deriver a thermal–hydraulic–mechanical coupling equation of CO₂-ECBM. The simulation results show that, as CO₂ injection pressure in CO₂-ECBM increases, the molar concentration and displacement time of CH₄ in the coal seam significantly decrease. With increasing injection temperature, the binary gas adsorption capacity in the coal seam decreases, and CO₂ reserves and CH₄ production decrease. High temperatures are therefore not conducive for CH₄ production.

First, the measuring principle, the weight function, and the magnetic field of the novel downhole inserted electromagnetic flowmeter (EMF) are described. Second, the basic design of the EMF is described. Third, the dynamic experiments of two EMFs in oil-water two-phase flow are carried out. The experimental errors are analyzed in detail. The experimental results show that the maximum absolute value of the full-scale errors is better than 5%, the total flowrate is 5–60 m³/d, and the water-cut is higher than 60%. The maximum absolute value of the full-scale errors is better than 7%, the total flowrate is 2–60 m³/d, and the water-cut is higher than 70%. Finally, onsite experiments in high-water-cut oil-producing wells are conducted, and the possible reasons for the errors in the onsite experiments are analyzed. It is found that the EMF can provide an effective technology for measuring downhole oil-water two-phase flow.

Oil-air-water three-phase flow patterns in small-diameter vertical measurement channels are complex, making it difficult to establish techniques for interpretation of logging information. In this study, dynamic experiments involving oil-air-water three-phase flows were performed using a novel production logging tool that combined a petal-type turbine flowmeter, a conductance sensor, and an optical fiber sensor in a simulation well. Sensor response characteristics were researched, and a new method of measuring the oil-air-water three-phase flow rate was proposed. The measurement range and resolution of the gas flow rate were 3 ∼ 20 m³/d and 1 m³/d, respectively, and the relative error range of gas flow rate interpretation was 5 ∼ 10%. The measurement range and relative interpretation error range of the total liquid flow rate were 10 ∼ 60 m³/d and 5 ∼ 10%, respectively. The measurement range and resolution of the water cut were 50 ∼ 100% and 2%, respectively. The absolute error range of interpretation of the water cut ranged from 3.2% to 5%. Currently, the technique is valid for laboratory use under ideal conditions.

Oil-water two-phase flow is widespread in petroleum industry processes. The study of oil-water two-phase flow in horizontal pipes and the liquid holdup measurement of oil-water two-phase flow are of great importance for the optimization of the oil production process. This paper presents a novel sensor, i.e., a mini-conductance probe (MCP) for measuring pure-water phase conductivity of oil-water segregated flow in horizontal pipes. The MCP solves the difficult problem of obtaining the pure-water correction for water holdup measurements by using a ring-shaped conductivity water-cut meter (RSCWCM). Firstly, using the finite element method (FEM), the spatial sensitivity field of the MCP is investigated and the optimized MCP geometry structure is determined in terms of the characteristic parameters. Then, the responses of the MCP for the oil-water segregated flow are calculated, and it is found that the MCP has better stability and sensitivity to the variation of water-layer thickness in the condition of high water holdup and low flow velocity. Finally, the static experiments for the oil-water segregated flow were carried out and a novel calibration method for pure-water phase conductivity measurements was presented. The validity of the pure-water phase conductivity measurement with segregated flow in horizontal pipes was verified by experimental results.

In the process of production logging interpretation, a water cut is one of the key factors to obtain the oil phase content in the oil well. In order to measure the water cut of the horizontal oil–water two-phase flow with low yield, the response characteristics of the combined capacitance sensor (CCS) are investigated under different flow patterns. Firstly, the measuring principles of coaxial, cylindrical, and CCS are introduced in detail. Then, according to the different flow pattern conditions of the horizontal oil–water two-phase flow, the response characteristics of the CCS are simulated and analyzed using the finite element method. Additionally, compared with the other two sensors, the advantages of the CCS are verified. Finally, the temperature and pressure calibration experiments are carried out on the CCS. The horizontal oil–water two-phase flow patterns in a low yield liquid level are divided in detail with a high-speed camera. Dynamic experiments are carried out in a horizontal pipe with an inner diameter of 125 mm on the horizontal oil–water two-phase flow experimental equipment. The simulation and experimental results show that the CCS has good response characteristics under different working conditions.

This article proposed a modified adaptive (MA) cross correlation method to measure the flow rate of high-water-cut oil-water two-phase flow. It asynchronously commences the acquisitions of the upstream and downstream signals for cross correlation according to the flow rate, enhancing the degree of correlation between them, thus a higher measurement accuracy of transition time can be obtained. By limiting the searching scope of the correlogram’s peak value in a transition time-related observation window, the calculation process is kept steady and divergence due to the outliers is effectively avoided. A planar flowmeter is adopted for high-water-cut flow rate measurement, and the advantages in axial resolution and sensitivity are analyzed. Experiments are conducted in 90% water cut oil-water flow in a practical vertical well. Results show that compared to the conventional (C) one, the MA method is capable of fast and reliable capture of the transition time from the upstream to the downstream sensors in a much wider flow rate range, with much lower deviation and a higher degree of correlation. Finally, the flow rates and their uncertainties are calculated from the measured transition time to validate the measurement stability.